Acoustic combining system



Aug. 30, 1932. H. H. BEVERAGE 1,874,865

ACOUSTIC .COMBIN-ING SYSTEM Filed Nov. 17. 1928 awww/woz mow n. savannas Patented Aug. 30, 1932 UNITED 1ST AT E s morn H. BEVERAGE, or Rimaniamo; NEW Your, assrenoa ro Immo COIQL c TION OF AMERICA, A CORPORATION (,)E' DELAWARE n V.ACOUSTIC COMBINING SYSTEM Application led lNovember 17 1928. Serial No. 320,017.'

This invention relates to diversity reception and more particularly to a method and means for combining the energies collected by the several antennae employed in divers. sity systems.

l Short Wave Vsignals are subject to fading' which varies both in frequency and degree in an unpredictable manner. Inasmuch as the fading vat any instant may ,differ very widely at geographically'spaced points, o r in different planes of polarization, it has been suggested that a receiving station be equipped with a number of antennaey having different fading characteristics, the energies collected by which are fed to a single signal respon"- sive means.

Experience has shown that high frequency energy fluctuates not only, in intensity but also in phase, and that there may be `conf o siderable relative phase fluctuation .at the several antennae. This phenomenon makes it impossible `to directly combine the radio frequency energies, for they energies may as often be -in phase opposition as in like phase. To overcome this difliculty it has been suggested to equip each of the antennae with a separate receiver, and to combine ythe ener? gies after rectification, and this, in the case of code signals, has proven an apt solution.

However, I have found that in the case of speech telephony, or other speech-simu# lating signals, where the transmission`r energy is radiated in the form of acarrier and side bands, there may be a relative difference in the phase fluctuations of .closely adjacent frequencies, such as side band and carrier fref quencies, even at one antenna, just as there is between carriers of like frequency` at different antennae. This causes similar phase fluctuations in the beat of the carrier and side'bands, for if of two beating Waves one is` kept constant in phase, while the Vother is shifted in phase, their beat is equally shifted in phase. l

This may readily be understoodA by visualizing two beating radio frequency waves of slightly different frequency, which have an envelope which is a maximum where .the waves are cophasal, and which gradually drops olf Ato a minimum lWhere the waves are in phase opposition, if `phaseV of one of these waves ijs kept constant while. the phase of the other is shifted degrees the Waves will be in phase opposition where before they were cophasalj,l so that the envelope will be a `rnin'mulflfl Where before it Was a maximum, and where the waves were in phase opposition they now willf4 cof phasal, so that the envelope will be a maxi-l mum where before it wasa minimum,` and, therefore, in effect the envelope too has been shifted 180 degrees in phase. Y y

Because of the foregoing considerations it follows that although the carrier andzside band .energies experience Onlyfradio'frequency differences inf phase, these differences are transferred to the` detected or audio frequency enerales,V so .thatait is impossible vto com-bine'the detected4 energiesl as it ris to directly combine theprig-inally collected radio frequency ener-gies.1` n l Another difliculty is that Aone variety of fading which often occurs is exceedingly rapid in frequency, at times almost approach.- ing a low audio'frequency. Neither volume control nor limiting can combat thisV type of fading, for they would then counteract the desired signal modulation.

The foregoing difliculties are especially important 'when' it is desired to rebroadcast received signals, Abecause for thisV purpose constant volume-and good quality are essen.-Y

tial, and to help obtain these characteristics is the object of my invention, `For this purpose I combine the collected energies acoustif cally, rather than electrically. `More in detail, my method includes simultaneously making a plurality of separate energy collections of relatively different fading` -characteristics, preferably'zby collecting .the radiated energy, at a plurality of `spaced points, separately detecting the collected energies, separately :translating the detected energies into sound energies, combiningthe sound ena` f ergles, transforming the combined soundfenergy into electrical energy, modulatingra'dio frequency energy by the electrical energy, andradating the modulated' energy. 4The combination'of the soundenergy is accom? ,plished in an acoustically insulated chamber lchanges in the audio frequency phase.

to considerably reflect and mix the sound energy therein, so that the resultant of the combination is more or less independent of The walls may be designed with a view toy softening and improving the quality of the sound,

Y apply volume control to the'ampliers of the Meanwhile ,the diversity receiving circuits. A Y reception inherently reduces and ordinarily eliminates the effect of rapid fading. Y

My invention is described more in detail in the following specification, which is accompanied by a drawing the single figure of which is a schematic wiring diagram for one form vof my invention.

Referring to the drawing it will be seen that there are a plurality of antennae 2, 4 and 6. Any desired number may be employed, and they are given relatively different fading characteristics in any suitable manner, such as by being geographically spaced, or by being positioned in different planes of polarization. The antennae are coupled by transmission lines 12, 14 and 16 to radiofrequency amplifiers 22,24 and 26, the amplified outputs from which are fed to autodyne heterodyne detectors 32, 34 and 36, in which the received vradio frequency energy is Vheterodyned to intermediate frequency energy', which in turn is amplified in the intermediate frequency amplifiersy 42, 44 and 46. A portionof the output from the intermediate frequency amplifiers is fed to suitable volume control detector circuits52, 54 and 56, of any conven` tional type, from which the bias leads 62, 64, and`66 run back to the control electrodes of the tubes of the amplifiers, in known manner.

The remainder of the 'intermediate frcquencyV energyl is le'dto detect-or and audio frequency amplifierstages 7 2, 74 and 76, the audio frequency outputs from which are separately .conducted over lines 82, 84,*and v86, to translating devices here exemplified by load speakers 92, 94, and 96 which, of course, have signal outputs of substantially they same frequency band width.v

' These speakers are located inside of a chamber 100, the lwalls ofy which are con-V structed kso asL to effectively sound insulate j the chamber. The volume is such that the soundfrom the speakers strikes the walls and is echoed and reflected to` a considerable eX- tent, in consequence of which the sound energy fromV theV various speakersY is well lmixed, so to speak.- This mixing is inltended to so upset the phase relations of the sound energy'that fluctuations in the relative phase ofthe audio frequency energies fed tothe speakers will be lessened in significanoe, insofar as their effect upon the in-V tegrated or resultant sound within the chambroadcasting station. f

It will be understood by those skilled in the art that many of the features described in the foregoing detailed arrangement are opas the modulating energy.4 Monitoring. speakers 110 and 112 may be respectively' located at the receiving station and at the e tional. For example, ythe number of an tennaeused, and howthey are givenrdifferent fading characteristics,may vary.'y The receivers'need not bel superheterodyne receivers, and if they are,vthe first detectors need not be autodyne detectors, for separate local oscillators and detectors may be used. rlhe volume controls may be arranged to control the gain in either the radio frequency or the intermediate frequency amplifiers alone, instead of in both, asf hasbeen indicated. The detectors usedfor obtaining the audio frequency energy 4for translation may be simultaneously used as the detectors for the volume control circuits, instead of employ ing separate detectors, as in the illustratedy arrangement. Furthermore, in its simplest form my invention needs no volume control, for its paramount factors are merelyia plurality of antennae having different` fading n 110, when a liighorder of quality is desired.

I claim:

1. AThe method of diversity reception of audible signals transmitted on'. a single high frequency carrier Ywhich includes collecting thedesired radiated signal energy at a plurality of spaced points, separately detecting the collected energies, eparately translating the detected energies .into sound energy, so directing and repeatedly reflecting the sound 'energiestliat they' are thoroughly mixed,

more or less independently of lthe initial audio frequency phase, transforming .the res sulting sound energy into electrical energy, and utilizing the electrical energy. i

2. The-method of ldiversity receptionY of audible signals transmittedA on a single 'high frequency carrier which includes collecting n the desired radiated signalenergyat apl'urality of spaced points, separately amplifying the collected energies, separatel controlling the gain in the step of ampli cation in response to the volume of the amplified energy to tend to keep the volume constant in order to obviate the effect of relatively slow fading, separately detecting the amplified ent fading characteristics, separately detecting the collected energies, separately translating the detected energies intoy sound energy, combining the sound energy, translating the combined sound energy into electrical energy, modulating radio frequency energy by the electrical energy, and radiating the modulated energy.

4. Therrmethod of rebroadcasting audible signals transmitted on a single high frequency carrier which includes collecting the radiated energy at a plurality of spaced points, separately amplifying the collected energies, separately controlling the gain in the step of amplification in response to the volume of the amplified energy to tend to keep the volume constant in orde-r to 'obviate the effect of relatively slow fading, separately detecting the amplified energies, separately translating the detected energies into sound energy, combining the sound energies With sufficient reflection and mixing to tend to obviate the eii'ect of audio frequency phase changes, transforming the resulting sound energy into electrical energy, modulating radio frequency energy by the resulting electrical energy, and radiating the modulated energy.

5. A diversity yreceiving system comprising a plurality of antennae adapted to receive a desired signal having different fading characteristics, means to separately detect the energies collected thereby, and means to acoustically combine the detected energies including an acoustically insulated chamber to reflect and mix the sound energy therein, and a plurality of reproducersvvithin the cham- 7 ber for separately translating each of the detected energies into sound energy of substantially like band Width.

6. A diversity receiving system comprising a plurality of spaced antennae collecting like energies collected thereby, and means to acoustically combine the detected energies including an acoustically insulated chamber to reflect and mix the sound energy therein, a plurality of reproducers Within the chamber for separately translating each of the detected energies into sound energy of like band Width, a microphone Within the chamber re- `sponsive to the resultant sound energy, and

means to utilize the electrical energy from the microphone. Y l 1 7. A diversity receiving system comprising a plurality of spaced antennae collecting sigv nal energy of like frequencies, means to separately amplify the energies collected thereby, a volume control for controlling the amplieffect of relatively slow fading, 4means to separately detect the amplified energies, an acousi tic combining system including an .acoustically insulated chamber to reflect and mix the 4,sound energy therein, aplurality of reproducers Within the chamber for separately translating each of the detected energies into sound energy of like band Width, a microphone responsive to the resultant sound energy, and means to utilize the electrical energy from the microphone.

- 8. A rebroadcasting system comprising a i plurality of antennae having different fading characteristics and collecting energy of like frequencies, means to separately detect the energies'collected thereby, means to separately translate the detected energies into sound energy, meansto combine the sound energy, a microphone responsive to the combined energy, and a broadcast transmitter the output from Which is modulated by the electrical energy vfrom the microphone.

9. A rebroadcasting system comprising a plurality of spaced antennae collecting energy of like frequencies, means to separately amplify the collected energies, a volume control for controlling the amplification gain in the amplifiers to obviate the effect of relatively slow fading, means to separately' detect the amplified energies., an acoustic combining system including an acoustically insulated chamber to reflect and mix the sound energy therein, a plurality `of reproducers Within the chamber for separately translating each of the detected energies into sound energya microphone responsive to the resultfication gain in the ampliers to obviate the Y ant sound energy, and a broadcast transmitter i HAROLD H. BEVERAGE.

Vsignal energy, means to separately detect Vthe 

